DiagnosisThe Caridea are the most speciose group of shrimps. Although the first and second pereiopods may or may not be chelate, the third pair are always chelate. It is quite easy to identify carideans, as they have the distinctive characteristic of a downturned bend in the third abdominal segment and both pleura of the second abdominal segment overlap their neighbours.
OriginOnly a few fossil forms exist which preserve the features necessary for phylogenetic positioning within extant clades, but it is thought that their origin lies in the Middle Jurassic (approximately 178 million years ago).
Image taken from www.nhm.org/guana/bvi-invt/bvi-surv/deca-inf.htm